Fluorescence is a photochemical phenomena in which a photon of specific light wavelength (excitation wavelength) strikes an indicator molecule, thereby exciting an electron to a higher energy state as a result of the collision. As that "excited" electron decays back down to its original ground state, another photon of light is released at a longer wavelength (emission wavelength).
Indicator molecules are specific in their excitation and emission wavelengths. The fluorescent emission from an indicator molecule may be attenuated or enhanced by the local presence of the molecule being analyzed. For example, a tris(4,7-diphenyl-1,10-phenanthroline)ruthenium (II) perchlorate molecule particular for oxygen sensing is excited by shining light onto the substance at 460 nm (blue). The molecules' fluorescent emission immediately occurs at 620 nm (orange-red). However, the emission is quenched by the local presence of oxygen interacting with the indicator molecule, to cause the intensity of the fluorescence to be related to the ambient oxygen concentration. Consequently, the more oxygen that is present, the lower the emission intensity and vice-versa and when zero or no oxygen is present, the maximum fluorescent intensity of emitted light is present.
These analytical techniques using fluorescent molecules as indicators have classically been used in fluorescence spectrophotometers. These instruments are designed to read fluorescence intensity and also the decay time of fluorescence. These devices typically cost 20,000 to 50,000 dollars and are used generally in research laboratories.
A second area of fluorescence sensor state-of-the-art is in fiber optic devices. These sensor devices allow miniaturization and remote sensing of specific analytes. The fluorescent indicator molecule is immobilized via mechanical means or chemistry to one end of an optical fiber. To the opposite end of the fiber is attached a fiber coupler (Y shaped fiber) or a beam splitter.
Incident excitation light is coupled into one leg of the fiber typically via a filtennd a lens. Excitation light is carried via the fiber to the distal end where the fluorescent indicator molecule is immobilized to the tip. Upon excitation, the indicator molecule uniformly radiates the fluorescent light, some of which is recaptured by the fiber tip and propagated back through the fiber to the Y junction or "coupler". At the junction, a substantial portion (typically half) of the fluorescence is conveyed back to the emitter or point of origin thereby unavailable for signal detection. To offset the inefficiencies of the system, lasers are often used to raise the input power and highly sensitive photomultiplier tubes are used as detectors thereby raising costs by thousands of dollars. The other half travels along the other leg of the Y to the detector and is recorded. A primary disadvantage with the system is the losses occurring at each fiber junction and via lenses and filters. The system is at a maximum 1-5% efficient with resultant loss in sensitivity and range. These devices have been demonstrated in the lab and are very recently available commercially for very limited applications. These devices differ from the previously mentioned fluorescence spectrophotometers in that they are dedicated to their specific application.
In view of the foregoing it is readily apparent that there are definite limitations associated with such prior art fluorescence devices including cost inefficiency and limitations related to use. In addition, such prior art fluorescence devices are complex with many separate parts and are bulky.
This invention overcomes these problems associated with prior fluorescence devices and provides a fluorescence device with greatly reduced costs and complexity as well as greatly improved efficiency. This invention provides a novel platform which greatly extends the use of fluorescent indicator molecules as a sensor allowing utilization, sensitivity and cost analyses not previously available. The invention also has increased uses and is easier to use as well as being more reliable than prior art fluorescence devices.